Eurex US, the troubled derivatives exchange, has been cleared to bring legal action against its US rivals over antitrust issues. It comes as the exchange prepares an exit strategy from the US.

The judge added: "The characterisations made in defendants' briefs are as close to the border of being misrepresentations to this court as it is possible to come without crossing it."

A CME spokesman told Reuters: "We continue to believe that this case is without merit and will continue to fight it vigorously."

CBOT officials could not be reached for comment. Eurex declined to comment.

Eurex US, which was launched in February 2004, brought the lawsuit against the CME and the CBOT in October 2003.

It charged its Chicago rivals with anti-competitive behaviour and unlawful attempts to block the entrance of a new competitor to the US market.

Last month shareholders asked Rudi Ferscha, chief executive of Eurex, to prepare a possible exit strategy from the US following poor volumes at the exchange. Their request came after he admitted the exchange had lost its battle with the Chicago Board of Trade for US Treasuries.

Eurex US's future will be decided in September.

The CBOT is preparing to float and expects to file an updated prospectus around September 1 that ammends the price range for its $150m (€122m) initial public offering, according to a filing with the Securities and Exchange Commission.